The invention relates to a method of manufacturing rolled wire rod having a combined silicon and manganese content greater than one and a half percent.
Steels of relatively high manganese and silicon contents are difficult to roll on modern high-speed wire rod rolling mills. This is especially the case when these mills are equipped with a modern wire rod adjuster for the accelerated cooling of the wire rod after rolling. Such a wire adjuster is, for example, a unit on which the wire rod is spread out in loops to cool down uniformly after rolling. The cause of the difficulty is the occurrence of brittle structural components consisting of martensite or bainite which seriously impair the drawing quality of wire rod. By the term, "steels of relatively high manganese and silicon content," as used herein, are meant steels in which the sum of the manganese and silicon contents amount to more than one and a half percent. The occurrence of the brittle structural components is also promoted by alloying components such as chromium and molybdenum. In steels which contain chromium and molybdenum, the above-given definition must be extended to the effect that the sum of manganese+silicon+chromium+molybdenum amounts to more than 1.5%. One especially important representative of these steels is what are known as CO.sub.2 welding rods, which are used for welding under carbon dioxide shielding gas. Their analysis commonly ranges from 0.80 to 1% silicon, 1.30 to 1.80% manganese, and 0.07 to 0.14% carbon. The composition of other steels in which difficulty is caused by the occurrence of brittle structural components is illustrated in the following Tables I to IV.
TABLE I ______________________________________ 0.05-0.20% carbon 0.50-1.50% silicon 0.80-3.00% manganese 0 -1.2% chromium 0 -0.30% titanium 0 -0.30% zirconium 0 -0.60% molybdenum 0 -0.40% vanadium 0 -0.50% copper 0 -1.50% nickel 0 -0.10% aluminum 0 -0.020% nitrogen 0 -0.040% sulfur 0 -0.040% phosphorous ______________________________________
Remainder iron+common impurities, the sum of the contents of silicon, manganese, chromium and molybdenum amounting to more than 1.5%.
TABLE II ______________________________________ 0.05-0.20% carbon 0.50-1.50% silicon 0.80-3.00% manganese 0 -0.25% chromium 0 -0.01% titanium 0 -0.05% molybdenum 0 -0.05% vanadium 0 -0.35% copper 0 -0.25% nickel 0 -0.02% aluminium 0 -0.015% nitrogen 0 -0.040% sulfur 0 -0.040% phosphorous ______________________________________
remainder iron+common impurities, the sum of the contents of silicon, manganese, chromium and molybdenum amounting to more than 1.5%.
TABLE III ______________________________________ 0.05-0.20% carbon 0.70-1.20% silicon 0.80-2.00% manganese 0 -0.15% chromium 0 -0.01% titanium 0 -0.05% molybdenum 0 -0.05% vanadium 0 -0.35% copper 0 -0.25% nickel 0 -0.02% aluminium 0 -0.015% nitrogen 0 -0.040% sulfur 0 -0.040% phosphorous ______________________________________
remainder iron+common impurities, the sum of the contents of silicon, manganese, chromium and molybdenum amounting to more than 1.5%.
TABLE IV ______________________________________ 0.06-0.14% carbon 0.70-1.00% silicon 1.30-1.60% manganese 0 -0.15% chromium 0 -0.01% titanium 0 -0.05% molybdenum 0 -0.05% vanadium 0 -0.20% copper 0 -0.15% nickel 0 -0.02% aluminium 0 -0.015% nitrogen 0 -0.040% sulfur 0 -0.040% phosphorous ______________________________________
balance iron+common impurities, the sum of the contents of silicon, manganese, chromium and molybdenum amounting to more than 1.5%.
It is known that in the foregoing steels the occurrence of brittle structural components is avoided if the rod cools very slowly after rolling. CO.sub.2 welding rod is consequently produced preferably on wire rod rolling mills in which a coil of wire rod weighing from 0.3 to 1 metric ton is wound on Edenborn reels at temperatures of around 800.degree. C. after rolling. The cooling down from this temperature takes place in these coils with extreme slowness, with the result that the formation of brittle structural components is prevented. Cooling in the coil, however, brings it about that the outer portions of the wire cool more rapidly than the inner portions. The quality of the wire rod cooled in the coil is therefore very irregular in comparison with the product of modern wire rod adjusters. This wire rod consequently does not have good drawing qualities.
A product of very good drawing qualities is produced when the rod is subjected to another annealing followed by very slow cooling. This annealing, however, involves considerably additional cost.